The present invention relates generally to automated testing of microelectric devices and particularly to computerized automated testing systems for microelectronic devices and the like in which it is desirable to measure the physical dimensions of the array of connectors on a microelectronic the device.
The dramatic increase in the production of microelectronic circuit devices and components such as integrated circuits using mass production methods has created a need in the art for high density, high speed, automated contactors to provide temporary testing connections to the micro electronic device contacts. While the structure of microelectronic devices varies considerably, most comprise a small circuit component or group of components supported on a small substrate. A plurality of electrical contacts on the substrate periphery are electrically connected to the circuit devices. During testing, probes or contacts are temporarily brought into contact with these peripheral contacts.
The majority of the testing systems devised to date for providing these temporary testing connections still rely upon the same basic mechanical technology previously utilized by the much larger printed circuit board testers and the like in that a group of metallic probes is mechanically positioned about the periphery of the device under test. in most such prior art testing systems, the alignment of the testing probe contactor and the appropriate contact on the device under test is achieved through the use of either precise control of the manufacturing process of the device and a coordinated precision on the placement of the testing probes, or in the alternative, precision optical systems under the control of an operator. In the latter system, manual adjustments of probe position are used to properly engage the desired contact for the device under test. In either system, little can be achieved with such testing devices beyond the temporary electrical connections and testing operation of device performance. That is to say, the present systems do not provide for a mechanical measurement of the geometry of the device under test.
The choice of which type of test system to be utilized is generally a choice between the need for speed versus the need for precision. The above-desired precision mechanical configuration provides speed of connection and testing and is often fully automatable but relies upon close mechanical tolerances to assure adequate electrical contact pressure for reliable connection and little can be done to compensate for geometric variations of the device under test. In addition, care must be taken to avoid or minimize over stressing of the device under test and the resulting mechanical damage to the device. This is made difficult in the absence of direct feedback of contact pressure. The optical systems described suffer some disadvantage in the speed of operation in that they are not fully automated. However, optical systems do permit or accept greater tolerance variations in the device under test. In either event, the prior art testing systems described do not accurately measure device geometry and do not readily establish consistent contact pressures independent of device geometry tolerance.
In another area of developing technology, the use of piezoelectric materials which provide the property of bilateral electromechanical transduction has emerged. For the most part, such piezoelectric materials have been utilized to produce electrically operable relay and switch structures in which mechanical motion of a contact or group of contacts is accomplished in response to a voltage applied to a piezoelectric element. Piezoelectric materials exist primarily in two forms. The first is referred to as a single crystal structure while the second is referred to as a ceramic or polycrystaline material. In either case, such piezoelectric materials include, among their other properties, a bilateral relationship between the deformation of the material (that is a change in geometry) and the applied electrical field. As an electromechanical transducer, the application of a electrical field to the piezoelectric material causes it to deform or change geometry. The change in geometry or deformation, is for any given material, predictable and is a function of the fabrication of the material and the orientation of its crystal structure. Conversely, the application of mechanical pressure to the piezoelectric material produces an electrical field. As a result, piezoelectric materials have the capability to impart mechanical motion to an attached object in response to an applied electrical field.
As mentioned, this property of piezoelectric materials has been utilized, for example, in U.S. Pat. No. 4,454,442 in constructing a euler lever piezoelectric relay. In the structure shown, a euler lever, which forms one contact of a contact pair, is captivated between a pair of piezoelectric members. A second stationary contact is positioned near the euler lever. A voltage is applied to either or both of the piezoelectric members causing deformation and a consequent altering of the configuration of the euler lever. This in turn results in a change in the distance between the contact on the euler lever and the stationary contact. Another switch structure utilizing a piezoelectric material is set forth in U.S. Pat. No. 4,093,883 in which a piezoelectric multimorph switch structure includes a laminated piezoelectric element which moves or bends in response to an applied voltage which creates a potential gradiant across the laminated element. Because of the multi-layered construction of the piezoelectric element, geometric deformation or changes of the piezoelectric materials results in creation of a bending motion. A contact born by the multi-layered piezoelectric material is selectively moved into or out of electrical connection with a second contact born on a second similarly configured piezoelectric multi-layered structure. The second piezoelectric structure is oriented in the opposite direction to the first piezoelectric structure and the thrust of U.S. Pat. No. 4,093,883 is to provide a structure which takes advantage of the opposite bending characteristics of the oppositely poled piezoelectric members to provide improved switching action and increased contact-to-contact pressure.
U.S. Pat. No. 4,403,166 sets forth a piezoelectric relay with oppositely bending bimorphs. A bimorph comprises a two layered piezoelectric structure which reacts to an applied voltage in a manner similar to the reaction of a bimetallic element to heat. The structure shown provides a piezoelectric relay which a pair of bimorph motors are supported in a cantilever fashion such that each bimorph has one end held in a fixed position while the other end remains free and is moved by the action bending of the piezoelectric bimorph elements. Contacts are supported upon the moveable ends of the cantilever bimorphs and, as a result, are brought into or moved from positions of connection with each other to produce a relay action.
While the prior art testings systems, such as those described above, provide some measure of either automated testing or precision. They do not provide for accurate high speed precision testing of microelectronic devices. Similarly, the presently used piezoelectric structures, such as those shown in the art and described above, provide for utilization of piezoelectric motors to move one or more electrical contacts in response to an applied signal. They do not, however, provide precision control of the location of contact and applied contact pressure required for structures which may be used to obtain the high speed mass production testing of microelectric devices. There remains therefore, a need in the art for a high speed precision controlled automated testing system suitable for use in testing microelectronic circuit devices.